A “ringing” gel is a specific type of gel, so designated because it has a firm jelly-like consistency that vibrates and returns to its original configuration when lightly tapped. The vibration can be felt with the hand when the container is held and tapped, and produces a bell-like resonance. This phenomenon is believed to be due to the entrapment of oil droplets, less than about 100 nm, within the nano-network structure of the gel. It has been suggested in U.S. Pat. No. 4,026,818 that the network consists of a rod-like lamellar structure connecting dispersed particles because this type of network allows the dispersed particles to vibrate within the gel, in a manner similar to the way a ball bounces off of the internal walls of a box containing a medium or a matrix.
Clear gel products are appealing and attractive to consumers. The wet appearance (i.e., like water) of clear gels makes it easy to believe that when applied, they in fact will feel the same way—refreshing, like a splash of water. Therefore, transparency of the clear gel is an important feature. It is also desirable for the feel of a clear gel to resemble water, and especially to feel like water when it is applied to the skin. Thus, the feel of the gel is also very important.
In general, gels are shear thinning materials composed of highly viscous materials. They tend to spread easily when force is applied to them. They have varying degrees of flowability when they sit for a long period of time. The term “gel” is defined as a semisolid colloid having one dispersing component that is a fluid. The dispersion fluid can be, for example, water which is present in a considerable quantity, usually greater than about 60 percent. A colloidal solution with water as the dispersion medium is known as a “hydrosol.” The aqueous system is usually thickened with agents such as acrylic polymers or gums to form the gel.
Specifically, ringing gels can be microemulsions or nanoemulsions. The microemulsion clear gel has an oil droplet particle size of about 0.01 to 0.08 microns and contains oil, water, and a high level of surfactants. The particle size of the oil droplet is small enough to allow light to pass through and create a translucent ringing gel. Conventional microemulsions are highly concentrated tenside-cotenside mixtures that achieve a minimum surface tension to stabilize the emulsion. The microemulsion is considered to be a transparent solution of micelles. The oil is dispersed in the network structure by surfactants, cosurfactants, and emulsifiers. The drawback to this system is that gels containing these ingredients can be irritating and feel sticky when applied to the skin.
Unlike microemulsions, nanoemulsions are metastable systems. Nanoemulsions comprise oil globules that have a mean particle size of less than 100 nanometers (nm). They have an appearance similar to water, and are known to feel like cream or milk. The nanoemulsion is a true emulsion because the oil droplets are dispersed in an aqueous phase. The structure of a nanoemulsion is dependent on the process used. Some examples of processes, include, PIT (phase inversion temperature) method or spontaneous emulsification or use of a high shear device. For example, it is described in U.S. Pat. Nos. 6,120,778, 5,753,241, and 5,152,923, incorporated herein by reference, to achieve a reduction in oil droplet size with the use of a high-pressure or high shear homogenizer. The fragile nature of nanoemulsions is believed to be related to the type of oil used, and the addition of polymers to thicken or to gel the nanoemulsion. Even when using high shear homogenizers, thickeners and surfactants are still necessary in the nanoemulsion formulation to aid in the thickening of the gel. They act at the interface of the oil and aqueous phase to support the nano-network structure of the gel. The physical conditions for a stable emulsion are maximum specific interface and maximum interficial energy of the particles.
In addition to certain physical conditions, the type of oil is also known to alter the integrity of a nanoemulsion. For example, in a publication entitled “Oil-in-Water Nanoemulsions: A new Type of Gallenic System”, XXIth IFSCC International Congress 2000, Berlin —Proceedings, by Sonneville-Aubrun et al., (“O/W Nanoemulsion Proceedings”) one of the major sources of instability in a nanoemulsion system is the nature of the oil and the addition of polymers to thicken or to gel the nanoemulsion. Thus, there remains a need to thicken compositions without incurring the drawbacks experienced with traditional thickeners, gelling agents, and emulsifiers. The present invention provides a stable emulsion while reducing the amount of surfactants, thickeners and emulsifier traditionally used to achieve the ringing nanogel composition.